Currently available alumina-based composites with high hardness, toughness, and strength which are intended for use at both ambient and elevated temperature applications are either expensive (silicon carbide-whisker reinforced alumina) or have limited toughness, typically considerable less than 5 MPam.sup. 1/2 (alumina with particulate second phase additions of titanium carbide, silicon carbide, boron carbide, etc.)
U.S. Pat. Nos. 4,919,718 and 5,015,290 pertaining to "Ductile Ni.sub.3 Al alloys as bonding agents for ceramic materials", and "Ductile Ni.sub.3 Al alloys as bonding agents for ceramic materials in Cutting Tools" described the use of nickel aluminide and other intermetallic alloys as additions to carbide, nitride, or oxide ceramics.
In a paper by T. Ekstrom, "Alumina Ceramics with Particle Inclusions", Jl. of the European Ceram. Soc., 12 (1993) 487-496, Ekstrom describes an alumina-based composite containing up to 30 wt. % Ti(C,N) and up to 5 wt. % nickel or nickel-molybdenum alloy additions. The composites were pressureless-sintered at 1750.degree. C. and hot-isostatically pressed at 1660.degree. C. with 200 MPa applied pressure.
In a paper by H. Mostaghaci, "Fabrication of Ceramics from Alumina and Ni-Based Alloys", Ceramics Transactions, Vol. 12, Ceramic Powder Science III, G. L. Messing, S. Hirano, and H. Hausner (eds.) Am. Ceram. Soc. (1990), the investigator describes alumina-based composites which were fabricated with the use of nickel alloys containing TiC additions. In this case, the investigator fabricated composites containing up to 25 vol % metallic content by pressureless sintering. No mechanical properties were reported, however, the TiC content (2.5 vol %) is probably not sufficient to retain high hardness.